Kauffmann’s prelude on “O heiliger Geist, o heiliger Gott” calls for the almost impossible combination of a Quintadena 16′ and Fagot 16′ in the left hand and a Vox Humana in the right hand. The Müller organ in Haarlem is not exactly a small organ, but I had to use a coupler not present in the real instrument to approach the sound Kauffmann intended. And even then I had to mimic the Vox Humana with the Oboe of the hoofdwerk.
But the result is very nice. There obviously is a lot to be learned in Kauffmann’s registration prescriptions.